This specification relates to an internal combustion engine in which cylinders contain pairs of opposed pistons. More specifically the specification concerns an opposed piston, compression ignition engine with two crankshafts in which the crankshafts have axes of rotation lying in a plane that is spaced apart from and parallel to a plane in which the axes of the cylinders lie. Each piston includes a piston rod coupled to one end of a connecting rod by a crosshead external to the piston. The other end of the connecting rod is coupled to a crank throw. The crosshead is constrained to maintain alignment with the piston rod by moving between fixed guides.
The classical opposed piston engine invented by Hugo Junkers includes two crankshafts, each disposed near a respective end of a rank of cylinders. The crankshafts are linked by connecting rods to respective pistons. Wristpins within the pistons couple the connecting rods to the pistons. In such an engine, the crankshafts operate with unequal torques, which produces substantial vibration in the long gear train coupling the crankshafts to the output drive.
An alternate opposed piston engine construction mounts the crankshafts beside the cylinders such that their axes of rotation lie in a plane that bisects the cylinders and is normal to the axes of the cylinders. Examples of this construction are found in U.S. Pat. No. 7,156,056 and US publication 2006/0157003, both commonly owned herewith. Such side-mounted crankshafts are closer together than those in the Junkers opposed piston engine. The crankshafts operate with equal torques and are coupled to an output drive by a shorter gear train than that of the Junkers engine. Each piston is coupled to both crankshafts by a mechanism including a piston rod coupled by an external pin to a pair of linkages. Each of the linkages is coupled to a respective one of the crankshafts. For each piston, one linkage includes a single connecting rod coupled to one crankshaft between two connecting rods of its opposed piston, and the other linkage includes two connecting rods coupled to the other crankshaft on either side of a single connecting rod of its opposed piston. Thus, each piston has three connecting rods. Since each piston is coupled to both crankshafts, the opposing lateral forces caused by the reciprocal motions of the two linkages cancel, thus avoiding side forces on the piston.
In this alternate construction the clearance between the sides of the cylinders and the side-mounted crankshafts with multiple connecting rods coupled thereto is low, which limits the space available for placement of fuel injectors and intake and exhaust manifolds on the cylinders. Moreover, since each piston has three connecting rods, the total number of connecting rods for all pistons adds substantially to the weight of the engine. Further, each crankshaft must be coupled to every pair of opposed pistons by three connecting rods, and the extra throws required for all of the connecting rods add weight and length to the crankshafts.
I have found that certain modifications of the alternative construction may reduce or eliminate these drawbacks and also yield other benefits. For example, location of both crankshafts on one side of the cylinders would free up space on the other side for an open engine architecture affording easy placement of and access to fuel injectors and intake and exhaust manifolds on the cylinders. Such single-side mounting of the crankshafts also permits the one side of the cylinders, with intake and exhaust manifolds mounted thereto, to be shielded from liquid splashed by operation of the crankshafts and connecting rods. Reduction of the number of connecting rods per piston would decrease the number of throws and thus the length required for each crankshaft. These reductions would decrease the weight and simplify the construction of the engine and crankshafts.